| With the energy issues becoming increasingly outstanding and the building energy consumption accounts for the proportion of the total energy consumption of society growing continually, the problem of building energy saving has become the hot topic in the world. In China, the measures of building energy saving always take the heat transfer in building envelope into consideration, and the heat transfer coefficient is tend to be a judging standard of the building energy conservation requirements. However, the effects of moisture transfer are not considered in these measures. Most of building envelope materials are porous media, its internal pores easily have wet component in the beginning of the building completed, and the interactions of heat and moisture transfer are highly coupled. Intensification of heat transfer changed with the change of moisture content in the walls, as well as the coefficient of thermal conductivity of materials. In consequence, it is certainly need for the study of the coupled heat and moisture transfer inside the building envelope, it has a very major impact on the thermal performance of the building materials, the building energy consumption and the building itself.The paper aims to study the coupled heat and moisture transfer dynamic characteristics of newly-completed building envelope. Both the situ test and numerical simulation are used in this paper, by analyzing the results of test data and numerical calculation, the conversion laws of temperature, moisture content and the heat transfer coefficient through a newly-completed building in Xi’an are studied.A detached building is built in situ field, installing with humidity measuring system, temperature measuring system and heat flow meter systems. The change of temperature, humidity inside the building envelope are traced and tested, the heat transfer coefficients of building envelope are tested regularly and the climate parameters in situ field also tested in real-time. Besides, the thermophysical parameters of building materials are calibrated in laboratory by appropriate test methods. A number of valuable data are obtained by these test. Based on the results of the thermophysical parameters and climate parameters in situ field, the coupled heat and moisture transfer dynamic analysis mathematical model for building envelope are developed by the software of CHAMPS, and the simulations are carried out with these models for 1~2 years.According to the test in situ and the numerical simulation, we found that the heat transfer through walls have the properties of decay and lag, the heat transfer is affected by the moisture transmission, so the temperature in center wall reach the peak first; Under this experimental condition, after the newly-completed building built for 264 days, the volumetric moisture content reduced gradually, the volumetric moisture content decline rate of the same kind of wall in different directions and the different kinds of walls are different, porous brick wall > aerated concrete wall> reinforced concrete wall, and he volumetric moisture content decline rate of north wall is greater than the east one. Due to the thermal insulation layer have got damp, the heat transfer coefficient increase first and then showed a trend of gradual decline, the actual heat transfer coefficient is always higher than the theoretical calculation value. According to the simulations for 2 years by employing the software of CHAMPS, we found that the volumetric moisture content have a periodical change with the trend of rises at first and the goes down; the decline rate of volume moisture content in the north aerated concrete wall and the north reinforced concrete wall are 61.54% and 61.54% respectively; the effective heat transfer coefficient of these two wall reduce to 1.12 times, 1.21 times theoretical value respectively.The paper aims at offering help to test the thermal performance of new building envelope on site. |
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